Fuser rolls used in electrostatic imaging systems generally comprise a cylindrical metal core coated with an elastomer such as Teflon™ (a ™ of DuPont). These fuser rolls are used in an imaging process wherein a photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the photoconductor surface. Toner is deposited onto the image charged photoconductor surface. The toner has a charge; thus, it will adhere to the photoconductor surface in the areas of the electrostatic latent image. The toner in image-wise configuration is then transferred to the paper or other medium. The toned paper is heated by the fuser roll system and the toner is fused to the paper to form a permanent image. The imaged paper is then passed to a document output collection area or tray where the user collects the finished copy.
The fusing components used in electrostatic imaging system generally comprise a toner station, a fuser roll(s), a pressure roll(s), a cleaning web(s) and a paper transport means. It is common that a back-transfer of cleaned toner from a fusers cleaning web to the fuser roll will occur, thereby causing marks—on copy (MOC). This defect is especially common with Teflon based fuser rolls and easily transferred toners. This MOC is a function of prior image history (low area coverages are worse) and a function of fuser roll voltage. This fuser roll contamination of toner or by-products of toner usually takes the form of a film, which eventually builds up and adversely affects the performance and life of the fusing components. Not only can fuser roll toner contamination affect the fusing components but will also affect the quality and clarity of the image on the paper in contact with the fuser roll. Also, in some instances the contamination of the fuser roll is eventually transferred to the cleaning web and lessens the cleaning web's cleaning effectiveness. In addition, all fusers have non-visible offset (NVO) to some level which can be higher for toners which transfer easily. Fuser rolls which have poor conformance may not transfer the NVO back to the paper and this NVO ultimately results in MOC, which is visually objectionable has to be cleaned from the fuser roll (FR). The MOC level is dependent on print history which is most likely due in part to the image wise and non-uniform residual wax left on the fuser roll in high image coverage areas and depletion of wax in low image coverage regions. The presently disclosed system provides an effective means to minimize the NVO by inducing a negative voltage on the fuser roll to repel negative toner, and the opposite polarity for positive toner.